The present invention relates to an image reading apparatus equipped with a scanner unit for optically reading originals placed on a platen, and particularly to suppression technology for electrical noise propagated by electrical cords or signal cords, and electromagnetic noise dispersed into the air (hereinafter referred to as ‘interference’).
Image reading apparatuses are ‘information technology devices such as information processing and electronic office devices’ subject to interference control in Japan. Therefore, such image reading apparatus interference levels are required to be controlled to below standardized values. Particularly in recent years, image reading apparatuses have been equipped with CPU and memory integrated circuits (IC) employing high frequency clock signals to read images on originals with high resolution. It is difficult to clear these strict interference standards in Japan or in other countries simply by applying interference measures of the same level as those conventionally applied.
On the one hand, plastic (compound) members are being used more often instead of conventional metal frames made from steel plates having shielding properties, for image reading apparatus frames. This is to reduce the manufacturing costs associated with image reading apparatuses by reducing the number of parts, and to lighten the apparatus weight. The use of plastic members increases the difficulty of suppressing the electromagnetic noise interference (called EMC measures).
FIG. 9 is a view of a conventional image reading apparatus (Japanese Patent Publication No. Hei 8-163291) that moves a scanner unit that optically reads originals placed on a platen 101, in a sub-scanning direction to read the images on the originals. The platen 101 is fastened to the upper portion of a metal frame 102 on the image reading apparatus and an original to be read is placed on the platen 101. A reading unit 103 for optically reading the originals is arranged below the platen 101 and is composed of a light source 103a, a line image sensor 103b and a lens 103c. The reading unit 103 is held by a carriage 104.
The carriage 104 moves reciprocally in the directions of arrows 109 and 110 (the sub-scanning direction) on a guide shaft 108 to read an original placed on the platen 101. The guide shaft 108 holding the carriage 104 is grounded by being integrated with the metal frame 102.
On the other hand, a guide shaft cannot be grounded by a frame in an image reading apparatus in which the guide shaft is fastened to a plastic frame. Therefore, a metal grounding member must be in contact with the guide shaft to enable the guide shaft to be grounded. If the guide shaft is ungrounded, the guide shaft acts as an antenna dispersing electromagnetic noise generated in the electronic circuits on the image reading apparatus. Electromagnetic noise affects the surrounding electronic devices and therefore, it is very important to ground the guide shaft in an image reading apparatus for EMC measures.
However, guide shaft supporting and guiding the reading unit (carriage) in the sub-scanning direction on an image reading apparatus must contact a grounding member in a way that will not interfere with the movement of the scanning unit. In the image reading apparatus disclosed in Tokkai Hei 8-163291, because the carriage 104 is supported on the guide shaft 108 at both ends of the scanning direction, the side surfaces of the carriage come near the frame when the carriage is positioned on a side of the scanning region. For this reason, it is necessary for an image reading apparatus supporting a guide shaft with the frame to ground the guide shaft by touching a metal grounding member to the guide shaft. However, not enough space is available to touch the grounding member and guide shaft.
Thus, it has been necessary to design image reading apparatuses allowing enough space to ground the guide shaft, even if the carriage is positioned on a side of the scanning region. This was performed by setting the supporting position to support the carriage guide shaft toward the inside. Also, when the supporting position of the carriage is determined for the grounding location, apparatus performance, such as the stability of carriage travel, is affected.
Thus, as described above, it has been necessary conventionally to design a grounding position for the guide shaft if the frame is made of plastic. This results in reducing the design freedom of such image reading apparatuses.
Also, when touching a grounding member to the guide shaft to ground it, one end of the grounding member touches the guide shaft, and the other is fastened by screws, etc., to the frame. This configuration simply increases the assembly time and the overall number of parts required.
It is an object of the present invention to increase design freedom of image reading apparatuses by enabling designs without requiring consideration for the grounding position of a grounding member and guide shaft to ground the guide shaft.
It is another object of the present invention to reduce the assembly time and the number of parts by reducing the number of steps to fasten a grounding member to a frame, etc., and fastening members such as screws.